Mutant of Arabidopsis Deficient in Xylem Loading of Phosphate

Abstract

A mutant of Arabidopsis thaliana deficient in the accumulation of inorganic phosphate has been isolated by screening directly for plants with altered quantities of total leaf phosphate. The mutant plants accumulate approximately 5% as much inorganic phosphate, and 24 to 44% as much total phosphate, as wild-type plants in aerial portions of the plant. Growth of the mutant is reduced, relative to wild type, and it exhibits other symptoms normally associated with phosphate deficiency. The phosphate deficiency is caused by a single nuclear recessive mutation at a locus designated phol. The rate of phosphate uptake into the roots was similar between mutant and wild-type plants over a wide range of external phosphate concentrations. In contrast, when plants were grown in media containing 200 micromolar phosphate or less, phosphate transfer to the shoots of the mutant was reduced to 3 to 10% of the wild-type levels. The defect in phosphate transfer to the shoots could be overcome by providing higher levels of phosphate. Transfer of sulfate to the shoots was essentially normal in the mutant, indicating that the phol lesion was not a general defect in anion transport. Movement of phosphate through the xylem of the shoots was not impaired. The results suggest that the mutant is deficient in activity of a protein required to load phosphate into the xylem.in uptake kinetics (3,7,11). Under conditions of limited phosphate availability, the capacity to transfer the absorbed phosphate to the shoots is also increased, suggesting an increase in phosphate release into the xylem (3, 7, 11). Compartmentalization of Pi appears to be important at the cellular level, with the vacuole acting as a storage site for excess Pi that can be released under conditions ofcytosolic Pi deficiency (3, 12). Thus, understanding the mechanisms that regulate Pi acquisition is complicated by both the existence of several potential sites of control and the presence of adaptive responses.As one approach to understanding how Pi levels are regulated, a genetic study was initiated to define loci that play a role in this process. The goal was to identify plants from a mutagenized population of Arabidopsis thaliana that display quantitative differences in leaf total phosphate content when compared with wild-type plants. We describe here the properties of a novel mutant that displayed a leaf Pi content that is only approximately 5% of the wild-type level. Measurements of the rate of root Pi uptake and transfer to the shoots, under various external phosphate concentrations and physiological conditions, indicate that the mutant is most likely deficient in activity of a protein required to load phosphate into the xylem.The mechanisms that regulate fluxes of phosphate between various tissues of higher plants are not well characterized. Potential points of control are the level of root Pi uptake, transfer of the absorbed Pi to the shoot, and compartmentalization into different subcellular organelles. There appear to be two major points of regulation for ion...

Integration of responses within and acrossArabidopsisnatural accessions uncovers loci controlling root systems architecture

“…We focused on a subset of 11 genes that each contain highly significant SNP associations (FDR: q < 0.05) (Table S2). Among these candidate genes is PHOSPHATE 1 or PHO1 (At3g23430) shown previously to play a role in inorganic phosphate loading into the xylem and aspects of root development (20,21). Several other uncharacterized genes were also identified.…”

Regulatory Network of MicroRNA399 andPHO2by Systemic Signaling

“…The pdr2 mutant is unable to maintain the root meristem activity specifically under Pi-deficient conditions because of the disruption of local Pi sensing (Ticconi et al, 2004). The pho1 mutant is impaired in the loading of Pi into xylem, which results in Pi-deficient symptoms in shoots (Poirier et al, 1991;Hamburger et al, 2002). In contrast to pho1, the pho2 mutant overaccumulates Pi in shoots as a result of enhanced Pi uptake and translocation (Delhaize and Randall, 1995;Dong et al, 1998).…”

A Member of the Heavy Metal P-Type ATPase OsHMA5 Is Involved in Xylem Loading of Copper in Rice

“…For example, AtHMA2 and AtHMA4 in A. thaliana and OsHMA2 in rice are responsible for xylem loading of Zn as well as Cd (Hussain et al, 2004;Verret et al, 2004;Yamaji et al, 2013). PHO1 in A. thaliana is involved in the transfer of inorganic phosphate from roots to shoots (Poirier et al, 1991;Chiou and Lin, 2011). BOR1 was reported to be a boron transporter for xylem loading in A. thaliana (Takano et al, 2002).…”